This invention relates to a method of forming, on a surface of a substrate, a pattern comprising a layer of metal oxide or a solid solution thereof, and to an electronic element or device, an optical element or device, and a circuit board each of which has a pattern formed thereby.
It is to be noted that the term xe2x80x9cmetal elementxe2x80x9d is herein used as a concept including a metaloid element, such as silicon. The term xe2x80x9cmetal oxidexe2x80x9d includes not only an oxide of a single metal but also a complex oxide and a solid solution containing these metal oxides as a main ingredient.
A method of depositing a thin film of a metal oxide on a surface of a substrate includes a vapor phase method such as a sputtering method, a CVD method, a vacuum evaporation method, and a cluster ion beam method, as well as a liquid phase method such as a sol-gel method. Conventionally, a patterned thin film having a fine interconnect pattern is obtained by forming a thin film on the entire surface of a substrate, patterning it through application of a resist material, exposure, and development, and thereafter etching the thin film, then removing the resist material.
In recent years, particularly in a semiconductor related field, fine patterning and stacking of interconnect patterns as well as an increase in thickness of a deposition film are required so as to accomplish a device which is small in size and light in weight. Specifically, following the development of a multilayered interconnect structure, desired is a method capable of achieving uniformity in film thickness and high dimensional accuracy so as to meet a high aspect ratio. To this end, in the vapor-phase thin film deposition method, a step coverage and a directivity are improved. However, this inevitably requires a special and expensive apparatus.
In the vapor phase method, such as the sputtering method, it is difficult to obtain a metal oxide thin film pattern of a wide area, due to such restriction imposed upon the apparatus that a closed space is required. In most cases, the process should be carried out at a high temperature, which restricts the species of the substrate. Furthermore, the dimensional accuracy can not be maintained due to the shrinkage of the metal oxide layer.
On the other hand, it is difficult in the sol-gel method to form a thin film of a complicated pattern. In addition, a heat treatment at a temperature not lower than 200xc2x0 C. is generally required to transform metal hydroxide formed from metal alkoxide into metal oxide crystals. During the treatment, the resist material which is inferior in thermal resistance is deteriorated so that the dimensional accuracy can not be maintained. The resultant thin film is liable to thermal deformation and cracks resulting from shrinkage. As a result, the substrate is restricted in its species and the dimensional accuracy can not be maintained due to the shrinkage of the metal oxide layer.
The present inventor has already proposed to deposit a thin film on a substrate surface from fluoro metal complex compound and/or metal fluoride without requiring any heat treatment but by means of the synthesis from aqueous solution, for example, a thin film of titanium oxide (Japanese Unexamined Patent Re-publication No. H10-11020; WO 98/11020); zirconium oxide, hafnium oxide, and rare earth oxide (Japanese Unexamined Patent Re-publication No. H08-28385; WO 96/28385); indium oxide-tin oxide solid solution (Japanese Unexamined Patent Publication No. H10-338523); perovskite-type complex oxide (Japanese Unexamined Patent Publication No. H08-310802); complex oxide containing rare earth element and/or alkaline earth element and copper within molecules (Japanese Unexamined Patent Publication No. H10-265220); zirconium titanate (Japanese Unexamined Patent Publication No. H10-87330).
However, no proposal has been made yet about a technique of obtaining a finely patterned thin film by the use of the above-mentioned synthesis from aqueous solution.
Thus, a method which is suitable for obtaining a finely patterned thin film of metal oxide, especially, a thin film having a wide area and/or a complicated shape is not found out yet.
It is an object of this invention to provide a method of readily forming, on a substrate surface, a fine pattern comprising a metal oxide layer and having an excellent uniformity and, especially, a fine pattern having a wide area and/or a complicated configuration without a high-temperature heat treatment.
It is another object of this invention to provide an electronic element or device, an optical element or device, and a circuit board, each of which has a pattern comprising such a metal oxide layer.
The present inventor repeatedly studied to achieve the above-mentioned objects and, as a result, found out that a fine pattern comprising a metal oxide layer can be obtained by forming a pattern by a coating material, thereafter depositing a metal oxide layer by the use of a synthesis from aqueous solution from a predetermined solution, for example, an aqueous solution of fluoro metal complex compound and/or metal fluoride, and then removing the coating material. This leads to completion of the present invention.
More specifically, according to this invention, there is provided a pattern forming method comprising the steps of:
(a) selectively forming a coating layer on a substrate surface,
(b) depositing, by the use of a predetermined solution, an oxide layer on both the coating layer and an uncoated part of the substrate surface which is not coated with the coating layer, and
(c) removing the coating layer and the oxide layer deposited on the coating layer to leave a desired pattern on the substrate surface.
As the predetermined solution used in the step (b) mentioned above, either an aqueous solution or a hydrofluoric acid solution of fluoro metal complex compound and/or metal fluoride containing at least one element selected from the group consisting of alkaline earth metal, transition metal, gallium, indium, silicon, tin, lead, antimony, and bismuth, can be used in the presence of a fluoride ion-capturing agent.
Furthermore, according to this invention, there are provided a pattern formed by the above-mentioned method as well as an electronic element or device, an optical element or device, and a circuit board each of which has the pattern.
Herein, it is noted that, in this invention, the term xe2x80x9cpatternxe2x80x9d means a design or a structure which is formed by a layer of a single metal oxide, a complex oxide, a solid solution containing the oxide as a main ingredient, or a mixture thereof. The pattern may be any design or structure including a dot, a straight line, a curve, a circle, a spiral, a symmetrical configuration, an asymmetrical configuration, or a combination thereof.
In this invention, the term xe2x80x9clayerxe2x80x9d covers various forms such as a cluster of particles, an aggregation of particles, a film, and a thin film, may be crystallized or amorphous, and may include a deposited or precipitated substance.